05 5.7, Cranks briefly, then stops

[AaronCarmichael]

I was driving to work a couple days ago, truck died on me (i think it was just a loose positive), but when I turned the key to start, motor cranks for a split second, fan just barely moves, probably only like 20 degrees max... Randomly when i came home from work today it started, but I haven't gotten it to do it a second time. I've had some time to look at it now, i've checked my grounds, tightened battery connections, put it on the charger, tried a different pcm, i do not have a clue at this point.

I tried jumping the starter with a screw driver and the motor cranks just fine but will not start